What is over-sleeping symptomatic for?

Last summer I had a period of about 4 months in which i felt like sleeping about 12-14 hours a day. In fact, I WAS sleeping 12-14 hrs a day. I wasn't under any medication, my diet was the same, I wasn't sick in any way. However, it wasn't normal and I'm curious if this can be considered a symptom of some ailment. Right now I'm back at sleeping 7 - 9 hrs/ night.